A tandem photoelectrochemical cell based on Cu2-xTe nanocrystals for solar energy conversion to hydrogen

Abstract

In this work we present the design, assembly and characterization of a tandem photoelectrochemical (PEC) cell based on two different crystallographic phases of sub-stoichiometric copper telluride nanocrystals (NCs). The first one, a pseudo-cubic phase, pc-Cu 2-x Te, is characterized by positive photocurrents, while the second one, a hexagonal phase, h-Cu 2-x Te, favors negative ones. Taking advantage of the different optoelectronic properties of the two Cu 2-x Te structures, we prepared a PEC cell composed of a hybrid pc-Cu 2-x Te/TiO 2 photoanode, with TiO 2 acting as a light absorber and electron selective layer, and a h-Cu 2-x Te/CuI photocathode, with CuI behaving as a photo-absorber and hole selective layer. The tandem PEC cell shows a photocurrent density of ∼0.5 mA/cm 2 when measured in a 2-electrode configuration without any co-catalyst. Finally, to test the PEC cell performance for the hydrogen evolution reaction (HER), a thin film of Pt was deposited on top of the photocathode and ∼7 μmol of hydrogen were obtained at 0.6 V in a 1-h experiment, reaching a photocurrent of 1 mA/cm 2 with no losses. • Investigating the optoelectronic properties of different Cu2-XTe crystallographic phases and using them as photoelectrodes for the first time. • Combining Cu2-XTe with TiO2 and CuI to build fully working hybrid photoelectrodes. • Building a functional Tandem PEC cell for hydrogen evolution reaction (HER).